#include <arpa/inet.h>
#include <errno.h>
#include <libgen.h>
#include <netdb.h>
#include <resolv.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>
#include <sys/wait.h>
#include <netinet/in.h>


#include <string.h>

#define BUF_SIZE 8192

#define READ  0
#define WRITE 1

#define DEFAULT_LOCAL_PORT    8080
#define DEFAULT_REMOTE_PORT   8081
#define SERVER_SOCKET_ERROR -1
#define SERVER_SETSOCKOPT_ERROR -2
#define SERVER_BIND_ERROR -3
#define SERVER_LISTEN_ERROR -4
#define CLIENT_SOCKET_ERROR -5
#define CLIENT_RESOLVE_ERROR -6
#define CLIENT_CONNECT_ERROR -7
#define CREATE_PIPE_ERROR -8
#define BROKEN_PIPE_ERROR -9
#define HEADER_BUFFER_FULL -10
#define BAD_HTTP_PROTOCOL -11

#define MAX_HEADER_SIZE 8192


#if defined(OS_ANDROID)
#include <android/log.h>

#define LOG(fmt...) __android_log_print(ANDROID_LOG_DEBUG,__FILE__,##fmt)

#else
#define LOG(fmt...)  do { fprintf(stderr,"%s %s ",__DATE__,__TIME__); fprintf(stderr, ##fmt); } while(0)
#endif


char remote_host[128];
int remote_port;
int local_port;

int server_sock;
int client_sock;
int remote_sock;




char *header_buffer;


enum {
  FLG_NONE = 0,
  R_C_DEC = 1,
  W_S_ENC = 2
};

static int io_flag;
static int m_pid;



void server_loop();
void stop_server();
void handle_client(int client_sock, struct sockaddr_in client_addr);
void forward_header(int destination_sock);
void forward_data(int source_sock, int destination_sock);
void rewrite_header();
int send_data(int socket, char *buffer, int len);
int receive_data(int socket, char *buffer, int len);
void hand_proxy_info_req(int sock, char *header_buffer);
void get_info(char *output);
const char *get_work_mode();
int create_connection();
int _main(int argc, char *argv[]);




ssize_t readLine(int fd, void *buffer, size_t n) {
  ssize_t numRead;
  size_t totRead;
  char *buf;
  char ch;

  if (n <= 0 || buffer == NULL) {
    errno = EINVAL;
    return -1;
  }

  buf = buffer;

  totRead = 0;
  for (;;) {
    numRead = receive_data(fd, &ch, 1);

    if (numRead == -1) {
      if (errno == EINTR)
        continue;
      else
        return -1;

    } else if (numRead == 0) {  /* EOF */
      if (totRead == 0)         /* No bytes read; return 0 */
        return 0;
      else                      /* Some bytes read; add '\0' */
        break;

    } else {

      if (totRead < n - 1) {    /* Discard > (n - 1) bytes */
        totRead++;
        *buf++ = ch;
      }

      if (ch == '\n')
        break;
    }
  }

  *buf = '\0';
  return totRead;
}

int read_header(int fd, void *buffer) {
  // bzero(header_buffer,sizeof(MAX_HEADER_SIZE));
  memset(header_buffer, 0, MAX_HEADER_SIZE);
  char line_buffer[2048];
  char *base_ptr = header_buffer;

  for (;;) {
    memset(line_buffer, 0, 2048);

    int total_read = readLine(fd, line_buffer, 2048);
    if (total_read <= 0) {
      return CLIENT_SOCKET_ERROR;
    }
    // 防止header缓冲区蛮越界
    if (base_ptr + total_read - header_buffer <= MAX_HEADER_SIZE) {
      strncpy(base_ptr, line_buffer, total_read);
      base_ptr += total_read;
    } else {
      return HEADER_BUFFER_FULL;
    }

    // 读到了空行，http头结束
    if (strcmp(line_buffer, "\r\n") == 0 || strcmp(line_buffer, "\n") == 0) {
      break;
    }

  }
  return 0;

}

void extract_server_path(const char *header, char *output) {
  char *p = strstr(header, "GET /");
  if (p) {
    char *p1 = strchr(p + 4, ' ');
    strncpy(output, p + 4, (int)(p1 - p - 4));
  }

}


// 转接端口到OpenVPN
int extract_host(const char *header) {
    char *_p = strstr(header, "Host");
    if (_p) {
    char host[] = "127.0.0.1";
    	strncpy(remote_host, host, (int)strlen(host));
    	remote_port = 443;
    }
  return 0;
}

int send_tunnel_ok(int client_sock) {
  char *resp = "HTTP/1.1 200 Connection Established\r\n\r\n";
  int len = strlen(resp);
  char buffer[len + 1];
  strcpy(buffer, resp);
  if (send_data(client_sock, buffer, len) < 0) {
    perror("Send http tunnel response  failed\n");
    return -1;
  }
  return 0;
}


void hand_proxy_info_req(int sock, char *header) {
  char server_path[255];
  char response[8192];
  extract_server_path(header, server_path);

  LOG("server path:%s\n", server_path);
  char info_buf[1024];
  get_info(info_buf);
  sprintf(response, "HTTP/1.0 200 OK\nServer: Proxy/0.1\n\
                    Content-type: text/html; charset=utf-8\n\n\
                     <html><body>\
                     <pre>%s</pre>\
                     </body></html>\n", info_buf);


  write(sock, response, strlen(response));

}

void get_info(char *output) {
  int pos = 0;
  char line_buffer[512];
  sprintf(line_buffer, "Welcome to use Kuaiyum.com Proxy.\n");
  int len = strlen(line_buffer);
  memcpy(output, line_buffer, len);
  pos += len;

  sprintf(line_buffer, "%s\n", get_work_mode());
  len = strlen(line_buffer);
  memcpy(output + pos, line_buffer, len);
  pos += len;

  if (strlen(remote_host) > 0) {
    sprintf(line_buffer, "start server on %d and next hop is %s:%d\n",
            local_port, remote_host, remote_port);

  } else {
    sprintf(line_buffer, "开启端口: %d\n", local_port);
  }

  len = strlen(line_buffer);
  memcpy(output + pos, line_buffer, len);
  pos += len;

  output[pos] = '\0';

}


const char *get_work_mode() {

  if (strlen(remote_host) == 0) {
    if (io_flag == FLG_NONE) {
      return "启动HTTP转发";
    } else if (io_flag == R_C_DEC) {
      return
        "start as remote forward proxy and do decode data when recevie data";
    }

  } else {
    if (io_flag == FLG_NONE) {
      return "start as remote forward proxy";
    } else if (io_flag == W_S_ENC) {
      return "start as forward proxy and do encode data when send data";
    }
  }

  return "unknow";

}

/* 处理客户端的连接 */
void handle_client(int client_sock, struct sockaddr_in client_addr) {
  int is_http_tunnel = 0;
  if (strlen(remote_host) == 0) { /* 未指定远端主机名称从http 请求 
                                     HOST 字段中获取 */

#ifdef DEBUG
    LOG(" ============ handle new client ============\n");
    LOG(">>>Header:%s\n", header_buffer);
#endif

    if (read_header(client_sock, header_buffer) < 0) {
      LOG("Read Http header failed\n");
      return;
    } else {
      char *p = strstr(header_buffer, "CONNECT"); /* 判断是否是http
                                                     隧道请求 */
      if (p) {
        LOG("receive CONNECT request\n");
        is_http_tunnel = 1;
      }

      if (strstr(header_buffer, "GET /proxy") > 0) {
        LOG("====== hand proxy info request ====");
        // 返回proxy的运行基本信息
        hand_proxy_info_req(client_sock, header_buffer);

        return;
      }

      if (extract_host(header_buffer) < 0) {
        LOG("Cannot extract host field,bad http protrotol");
        return;
      }
      LOG("Host:%s port: %d io_flag:%d\n", remote_host, remote_port, io_flag);

    }
  }

  if ((remote_sock = create_connection()) < 0) {
    LOG("Cannot connect to host [%s:%d]\n", remote_host, remote_port);
    return;
  }

  if (fork() == 0) {            // 创建子进程用于从客户端转发数据到远端socket接口

    if (strlen(header_buffer) > 0 && !is_http_tunnel) {
      forward_header(remote_sock); // 普通的http请求先转发header
    }

    forward_data(client_sock, remote_sock);
    exit(0);
  }

  if (fork() == 0) {            // 创建子进程用于转发从远端socket接口过来的数据到客户端

    if (io_flag == W_S_ENC) {
      io_flag = R_C_DEC;        // 发送请求给服务端进行编码，读取服务端的响应则进行解码
    } else if (io_flag == R_C_DEC) {
      io_flag = W_S_ENC;        // 接收客户端请求进行解码，那么响应客户端请求需要编码
    }

    if (is_http_tunnel) {
      send_tunnel_ok(client_sock);
    }

    forward_data(remote_sock, client_sock);
    exit(0);
  }

  close(remote_sock);
  close(client_sock);
}

void forward_header(int destination_sock) {
  rewrite_header();
#ifdef DEBUG
  LOG("================ The Forward HEAD =================");
  LOG("%s\n", header_buffer);
#endif

  int len = strlen(header_buffer);
  send_data(destination_sock, header_buffer, len);
}

int send_data(int socket, char *buffer, int len) {

  if (io_flag == W_S_ENC) {
    int i;
    for (i = 0; i < len; i++) {
      char c = buffer[i];
      buffer[i] ^= 1;

    }
  }

  return send(socket, buffer, len, 0);
}

int receive_data(int socket, char *buffer, int len) {
  int n = recv(socket, buffer, len, 0);
  if (io_flag == R_C_DEC && n > 0) {
    int i;
    for (i = 0; i < n; i++) {
      char c = buffer[i];
      buffer[i] ^= 1;
      // printf("%d => %d\n",c,buffer[i]);
    }
  }

  return n;
}



/* 代理中的完整URL转发前需改成 path 的形式 */
void rewrite_header() {
  char *p = strstr(header_buffer, "http://");
  char *p0 = strchr(p, '\0');
  char *p5 = strstr(header_buffer, "HTTP/"); /* "HTTP/" 是协议标识 如
                                                "HTTP/1.1" */
  int len = strlen(header_buffer);
  if (p) {
    char *p1 = strchr(p + 7, '/');
    if (p1 && (p5 > p1)) {
      // 转换url到 path
      memcpy(p, p1, (int)(p0 - p1));
      int l = len - (p1 - p);
      header_buffer[l] = '\0';


    } else {
      char *p2 = strchr(p, ' '); // GET http://3g.sina.com.cn HTTP/1.1

      // printf("%s\n",p2);
      memcpy(p + 1, p2, (int)(p0 - p2));
      *p = '/';                 // url 没有路径使用根
      int l = len - (p2 - p) + 1;
      header_buffer[l] = '\0';

    }
  }
}


void forward_data(int source_sock, int destination_sock) {
  char buffer[BUF_SIZE];
  int n;

  while ((n = receive_data(source_sock, buffer, BUF_SIZE)) > 0) {

    send_data(destination_sock, buffer, n);
  }

  shutdown(destination_sock, SHUT_RDWR);

  shutdown(source_sock, SHUT_RDWR);
}



int create_connection() {
  struct sockaddr_in server_addr;
  struct hostent *server;
  int sock;

  if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
    return CLIENT_SOCKET_ERROR;
  }

  if ((server = gethostbyname(remote_host)) == NULL) {
    errno = EFAULT;
    return CLIENT_RESOLVE_ERROR;
  }
  LOG("======= forward request to remote host:%s port:%d ======= \n",
      remote_host, remote_port);
  memset(&server_addr, 0, sizeof(server_addr));
  server_addr.sin_family = AF_INET;
  memcpy(&server_addr.sin_addr.s_addr, server->h_addr, server->h_length);
  server_addr.sin_port = htons(remote_port);

  if (connect(sock, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
    return CLIENT_CONNECT_ERROR;
  }

  return sock;
}


int create_server_socket(int port) {
  int server_sock, optval;
  struct sockaddr_in server_addr;

  if ((server_sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
    return SERVER_SOCKET_ERROR;
  }

  if (setsockopt
      (server_sock, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval)) < 0) {
    return SERVER_SETSOCKOPT_ERROR;
  }

  memset(&server_addr, 0, sizeof(server_addr));
  server_addr.sin_family = AF_INET;
  server_addr.sin_port = htons(port);
  server_addr.sin_addr.s_addr = INADDR_ANY;

  if (bind(server_sock, (struct sockaddr *)&server_addr, sizeof(server_addr))
      != 0) {
    return SERVER_BIND_ERROR;
  }

  if (listen(server_sock, 20) < 0) {
    return SERVER_LISTEN_ERROR;
  }

  return server_sock;
}

/* 处理僵尸进程 */
void sigchld_handler(int signal) {
  while (waitpid(-1, NULL, WNOHANG) > 0);
}

void server_loop() {
  struct sockaddr_in client_addr;
  socklen_t addrlen = sizeof(client_addr);

  while (1) {
    client_sock =
      accept(server_sock, (struct sockaddr *)&client_addr, &addrlen);

    if (fork() == 0) {          // 创建子进程处理客户端连接请求
      close(server_sock);
      handle_client(client_sock, client_addr);
      exit(0);
    }
    close(client_sock);
  }

}

void stop_server() {
  kill(m_pid, SIGKILL);
}

void usage(void) {
  printf("Usage:\n");
  printf(" -l <port number>  specifyed local listen port \n");
  printf(" -h <remote server and port> specifyed next hop server name\n");
  printf(" -d <remote server and port> run as daemon\n");
  printf("-E encode data when forwarding data\n");
  printf("-D decode data when receiving data\n");
  exit(8);
}

void start_server(int daemon) {
  // 初始化全局变量
  header_buffer = (char *)malloc(MAX_HEADER_SIZE);

  signal(SIGCHLD, sigchld_handler); // 防止子进程变成僵尸进程

  if ((server_sock = create_server_socket(local_port)) < 0) { // start server
    LOG("开启代理失败: %d\n", local_port);
    exit(server_sock);
  }

  if (daemon) {
    pid_t pid;
    if ((pid = fork()) == 0) {
      server_loop();
    } else if (pid > 0) {
      m_pid = pid;
      LOG("Proxy 进程号: [%d]\n", pid);
      close(server_sock);
    } else {
      LOG("Cannot daemonize\n");
      exit(pid);
    }

  } else {
    server_loop();
  }

}

int main(int argc, char *argv[]) {
  return _main(argc, argv);
}

int _main(int argc, char *argv[]) {
  local_port = DEFAULT_LOCAL_PORT;
  io_flag = FLG_NONE;
  int daemon = 1;

  char info_buf[2048];

  int opt;
  char optstrs[] = ":l:h:dED";
  char *p = NULL;
  while (-1 != (opt = getopt(argc, argv, optstrs))) {
    switch (opt) {
    case 'l':
      local_port = atoi(optarg);
      break;
    case 'h':
      p = strchr(optarg, ':');
      if (p) {
        strncpy(remote_host, optarg, p - optarg);
        remote_port = atoi(p + 1);
      } else {
        strncpy(remote_host, optarg, strlen(remote_host));
      }
      break;
    case 'd':
      daemon = 1;
      break;
    case 'E':
      io_flag = W_S_ENC;
      break;
    case 'D':
      io_flag = R_C_DEC;
      break;
    case ':':
      printf("\nMissing argument after: -%c\n", optopt);
      usage();
    case '?':
      printf("\nInvalid argument: %c\n", optopt);
    default:
      usage();
    }
  }

  get_info(info_buf);
  LOG("%s\n", info_buf);
  start_server(daemon);
  return 0;
}